Process of electrodepositing indium



Patented Sept. 12, 1944 I UNITED STATES, PATENT OFFICE I PROCESS OF EfZEfiODEOSITING Albert J. Phillips, Plainfield, and Henry B.

Linton-d, Woodbridge, N. .L, assignors to Ameri-' can Smelting and Refining Company, New York, N. Y., a. corporation of New Jersey Application March 2, 1940, Serial No. 321,839

(Cl. 2044l5) aClziims.

The present invention deals with certain improvements in the electrodeposition of indium. It is known in the art to electroplate indium from cyanide baths or chloride baths with the use of suitable addition agents, it being considered essential for the production of adherent deposits of indium that the baths be either a cyanide or chloride bath. However, in the operation of such baths, there arc difficulties, owing, for instance to the instability of the cyanide electrolyte, and anode corrosion due' to chlorine evolution, from the chloride electrolytes.

In the prior art operations for the electrodeposition of indium, either in refining or plating operations, care has been taken to avoid sulphate electrolytes owing to the diificulty. or

a controlled pH value of the sulphate bath between definite limits, which limits are found in practice to bev in the range of from about pH 1.5 and pH 3,4, it beingfound that the maintenance of this controlled pH value results in the producriodically a portion of the electrolyte and reimpossibility of obtaining uniform deposits of indium from such sulphate electrolytes, the deposit of indium, if formed at all, being of a spongy and non-adherent character.

The present invention provides an improved process for electrodepositing indium either in refining or plating operations, wherein a smooth,

adherent deposition of indium is effected by the electrolysis of a solution of indium sulphate, thereby avoiding the difficulties incident to the use of cyanide or chloride electrolytes.

Apparently, the difllculty of producing satisfactory deposits of indium from the electrolysis of sulphate electrolytes resides in the fact that during the electrolysis the acidity of the sulphate solution changes very rapidly, this condition having been observed to take place during the investigations leading up to the present process, the early stages of the investigation producing the same spongy deposit of indium which were noted in the prior art in connection with the electrolysis of indium sulphate solution.

It has been found, however, in the investigations which resulted in the present improved process,,that very satisfactory deposits of indium are-obtainable from indium sulphate electrolytes, even without the use of addition agents or buffers, if the acidity of the electrolyte is maintained between carefully controlled limits, under properly controlled operating conditions,

there being obtained the dense crystalline and properly.

One of the important factors in the practicing placing with Water to maintain the indium-ion concentration at its original value. Where insoluble anodes are employed, it may be desirable to control the acidity of the electrolyte between proper limits by withdrawing a portion thereof as the electrolysis proceeds, adding to the withdrawn portion a suitable quantity of indium hydroxide which quantity is determined by the pH value of the solution, so that when the thus-treated withdrawn portion is reintroduced into the cell, the proper pH value will be maintained. The withdrawn portion of the electrolyte may be filtered after this treatment with the indium hydroxide, and the volume madeup with any necessary addition of water.

Because of the necessity of treating the elec-. trolyte in such a manner as has been described above where either insoluble or soluble anodes are used for the electrolysis, it is preferred to carry out the process by using both insoluble and soluble anodes. Such anodes may be employed in the same cell, or the soluble and insoluble' anodes may be placed in separate cells with an intercell circulation of the electrolyte being-maintained. The soluble anodes of course are formed from metallic indium, the insoluble anodes being, suitably, platinum.

The indium content of the electrolyte may vary between wide limits, the process having been operated successfully with a range of from 5 grams per liter of indium to 130 grams per liter of indium, the pH value of the electrolyte of course being controlled in accordance with the concentration of indium in the solution, the higher concentrations of indium being operated in connection with the lower limits of the pH control, and low concentrations of indium being operated with the higher pH values, it being of the present improved process is to maintain important to maintain sufiicient acidity in the electrolyte to prevent precipitation of the in-. dium by hydrolysis.

It is desirable to maintain the electrolyte in circulation, by stirring in the cell, or by extracell circulation. The electrolysis may proceed at room temperatures, although slightly elevated temperatures seem to give slightly better deposits in some cases.

The electrolysis is carried out with a cathode current density of a wide range, the process having been carried out with cathode current density ranging all the way from 2 amps/sq. ft. to 40 amps/sq. ft., it being found in practice, however,

, that a cathode current density of about 2.4

amps/sq. ft. for refining, and about 30 amps/sq.

ft. for plating gives the best results.

The anode current density also is variable. In refining operations, the current density depends on the purity of the anode, but is kept as low as possible, the best range being from approximately 2 to 4 amps/sq. it. In plating operations, with no thought to purification of the deposit, the anode current density may be very high, in practice, for example, 40 amps/sq. ft. or higher.

The cell employed is an undivided cell, and the soluble anodes may be enclosed in a bag if desired, or the operation may be conducted without a bag around the anodes. In the latter instance the electrolyte must be filtered from time to time to remove slimes from the bottom of the cell.

The usual arrangement of electrodes is employed.

The accompanying drawing illustrates typical simple cell installations which'may be used in carrying out the present improved process, it being understood, however, that the particular illustrated showings may be modified quite widely without efiecting the electrolysis proceeding in the cells, the views of the drawing showing -merely examples of the simplest arrangements of apparatus suitable for carrying out the process.

In the drawing, Fig. 1 represents a type of wiring diagram suitable for use with a combination of soluble and insoluble anodes in the same cell, there being a plurality of cells shown in series.

Fig. 2 is a view similar to Fig. 1, wherein the soluble and insoluble anodes are grouped in separate cells, there being provided inter-cell circulation for the electrolyte.

Referring more particularly to the drawing, and first to Fig. 1, two electrolytic cells- 4 and 6 are shown, which cells contain an electrolyte 8 of indium sulphate. a soluble anode I0 and an insoluble anode l2, the anodes l0 and I2 having a cathode l4 placed between them.

These electrodes of course are of suitabl shapes and sizes and their number may be varied at will. The refe'rencecharacters in cell 4 are primed to avoid confusion.

A suitable electrolyzing current is supplied to the cells from a source l6 of direct current, the

anodes of cell 6 being connected to the positive.

side of the current source I6, the insoluble anode l2 of cell 6 being connected to the positive side ofthe current source by current leads l8 and 26 through an ammeter 22, while the soluble anode I8 is connected to the positive side of thecurrent source through lead 24, adjustable re sistance 26 and lead 28.

The cathode 14 of cell 6 is connected by suitable leads 38, 32, 34 to the insoluble anode I2 of cell 4, through, an ammeter 36, and also to the soluble Either cell 4 or 6 contains also the power source.

In Fig. 2, there is indicated an arrangement wherein the soluble anodes and insoluble anodes are in separate cells, with inter-cell circulation means. In the system of Fig. 2., there are shown two cells 54 and 56, the cell 54 receiving the soluble anodes 5B, and the cell 56 receiving the insoluble anodes 60. Cathodes 62, 62 are positioned between the anodes.

A suitable source of direct current l6 has its positive side connected to the soluble anodes 58 in cell 54 and to the insoluble anodes 60 of cell 56. The connections to the soluble anodes are made through leads 63, 64, ammeter 66 and leads 68 and 16, the latter being branched as required for requisite anodic connections. The positive side of the current source is connected also with the insoluble anodes 60 through leads 63, I2, "ammeter l4 and lead 16, which is branched as required for requisite anodic connections.

The cathodes 62 in the cell 54 are connected by leads 'l8, adjustable resistance and lead 82 to the return side of the current source, and the cathodes 62 in the cell 56 are connected in the return side of the current source through lead 84, adjustable resistance 66, and lead 88.

The cells are interconnected as shown at and electrolyte is withdrawn from cell 56 through pipe 92 by pump 94 and delivered by the pump 94 into cell 54 by way of pipe 96.

In Fig. 2, the ammeter 66 measures total current in the cell 54 and the ammeter 14 measures the total current in cell 56.

Obviously, arrangements of equipment other than these herein specifically illustrated may be employed, with comparable electrolytic results being obtainable. Thus, it is possible, easily, to form the electrical circuits in such a way as to require the use of only one, or at most two, ammeters, instead of the larger number show in the illustrated circuits.

The process is illustrated by the following specific example, which illustrates the conditions of electrolysis in a typical run: Two cells were used, the electrolyte being" circulated between them,

one of the cells containing soluble anodes of indium, the other cell containing insoluble anodes composed of platinum.

In refining operation, in the soluble anode cell there was maintained a current density of 2.4.

amps/sq, it. at both anod and cathode. The

voltage drop was from 0.45 to 0.6 volt.

In the insoluble anode cell, the current strength talline deposit being obtained. The current efficiency was from 95 to and the indium content of the electrolyte was maintained at 18.2 grams per liter of indium as indiumsulphate.

In plating, a pH value the same as above was maintained by the same ratio-of soluble to insoluble anode current strengths. With a cathode If desired, one or mor oi! the alkali sulphates such as sodium sulphatewor ammonium sulphate, in effective amounts, say 25 gms./liter may be added to the electrolyte for reducing the resistance thereof, with no bad eflects on the deposit;

also insoluble colloidal organic addition agents,

such as glue or gelatin may be incorporated in the electrolyte for facilitating smoothness in heavy deposits.

What is claimed is:

1. A process of electrodepositing indium metal on a cathode surface which comprises passing electric current through a prepared electrolyte solution consisting of an aqueous solution of indium sulphate and sulphuric acid, said solution containing'from 5 to 130 grams of indium per liter of electrolyte, using soluble indium anode and insoluble anodes with cathode electrodes under pH controlled conditions inor'der to form a dense, coherent crystalline deposit of metallic indium on-the cathode, and wherein the pH value of said electrolyte is maintained between 1.5 and 3.4 during electrolysis by means of said soluble and insoluble anodes to causethe deposition of a smooth adherent deposit of indium on the surface of the cathode. 1

2. A process of electrodepositing indium metal on a cathode surface which comprises passing electric current through a prepared electrolyte.

solution consisting of an aqueous solution of indium sulphate and sulphuric acid,'which solution contains about 18.2 grams of indium per liter,

using soluble indium anodes and insoluble anodes with cathode electrodes under pH controlled conditions so as to form a dense crystalline deposit of indium on the cathode, 'said pH value being controlled within the range of from 2.1 to

2.3, during electrolysis by m ans of said soluble and insoluble anodes to cause the formation of a smooth, continuous and adherent deposit of indium metal on said cathode surface. a

3. A process of electrodepositing indium metal on a cathode surface which comprises providing an electrolyte solution composed of indium sulphate dissolved in aqueous sulphuric acid and wherein the indium content pf said electrolyte solution approximates about 18.2 grams per liter, passing electric current through said solutions under pH controlled conditions using soluble indium anodes and insoluble anodes and cathode electrodes with a cathode current density of between 2 and 40 amperes/sq. it. to cause the indium to be deposited out on the cathode, and during said deposition maintaining the pH value of the {indium sulphate solution between 1.5 and 3.4 by means of said soluble and insoluble anodes where- 

